Bed coverings are generally designed to keep a resting person from becoming uncomfortably cool. Active bed coverings, such as electric blankets, accomplish this goal by generating heat. Comforters, blankets, sheets, and other passive bed coverings are generally designed to keep a resting person warm by slowing the loss of body heat to the surroundings. Bed coverings must, however, also allow transmission of a certain amount of body heat to avoid overheating. Most households therefore use lighter-weight bed coverings during warmer weather and different, heavier coverings in cooler weather.
To avoid the need for different coverings for warm and cool weather use. inventors have designed a variety of adjustable-warmth bed coverings. Some adjustable-warmth bed coverings are multiple-zone bed coverings that allow the users to vary the degree of heat retention over different zones of the bed. These multiple-zone bed coverings are particularly useful in allowing variation in heat retention for multiple, simultaneous users or multiple zones on a single user. When two people sleep in a bed, the standard bed coverings that one person finds comfortable may be too hot or cool for the other person. Each person may also find that his or her torso is too warm when a sufficiently thick blanket or other standard bed covering is used to prevent his or her feet, for example, from getting cold. By allowing variation of the heat retention characteristics of different zones of the bed covering, a bed covering can be adjusted to allow each occupant to be comfortable.
U.S. Pat. No. 3,331,088 issued to Marquette (the "Marquette Patent") describes an adjustable-warmth blanket with changeable, detachable top panels that permit the user to achieve the thickness or thinness of the covering desired. The Marquette blanket includes a separate panel that can be attached to the foot portion of the blanket for keeping a person's feet warm. The panels are attached to the blanket using fastening means such as a slide fastener, buttons, eyelets, or laces.
U.S. Pat. No. 5,187,825 issued to Tesch sets forth at least one embodiment of a quilted bed blanket with a plurality of chambers, each individual chamber having an associated opening. Varying degrees of warmth can be obtained by changing the amount of a loose filling material, such as aggregates of spherically wrapped fibers, in each chamber.
U.S. Pat. No. 4,839,934 issued to Rojas (the "Rojas Patent") describes a multiple component comforter quilt providing varying degrees of heat retention in different zones. The Rojas multiple component comforter quilt utilizes pockets into which insulating material can be inserted. Materials of varying insulation qualities can be used with such a pocketed bed covering to provide zonal variation of heat retention characteristics. Specifically, Rojas discloses a container-cover unit containing removable and interchangeable insulator pad units, enclosing heat insulating material such as down. The container-cover can be made of decorative fabrics. An embodiment of the invention described in that patent uses substantially square insulator pads of different heat insulating characteristics to form selective heat insulation zones.
U.S. Pat. No. 2,248,768 issued to Licht (the "Licht Patent") is directed to a pocket form comforter that may include pockets into which forms containing filling materials may be placed. The forms and pockets are shaped in such a manner that the forms are substantially adjacent to each other.
It is notable that none of the adjustable-warmth bed coverings found in the prior art have met with widespread commercial success. All suffer from a number of drawbacks that make their marketing and use impractical. As a result, none are currently marketed in the United States.
One significant drawback of the coverings of the prior art is that they require the user to maintain a substantial inventory of insulating materials of varying heat-retention qualities, only some of which are likely to be in use at any time. This drawback is particularly characteristic of the Rojas and Licht Patents.
Another drawback of the coverings of the prior art is that they are intended to be used as outer coverings. If such coverings were to become commercially available, they would likely be available in only a limited number of fabric designs, making it less likely that a consumer would be able to find an adjustable warmth bed covering that matched the consumer's tastes or home decor.
Yet another drawback of the coverings of the prior art is that their designs generally result in a bed covering having gaps between the different pockets or insulating materials used to provide zonal variation of heat retention characteristics. As a result, the coverings result in "cold spots" that make them less desirable than standard, uniform bed coverings. Although the design described in the Licht Patent avoids gaps by using boxed pocket and insulator form covers, the design suffers from the manufacturing obstacles described below.
Another significant drawback of the coverings of the prior art is that they are difficult or expensive to manufacture. For example, the covering described in the Licht Patent requires both insulator pads and pockets to have boxed comers. As another example, the Rojas Patent describes a covering into which closing flaps or tapes must be incorporated. In addition to increasing manufacturing costs, these requirements make the coverings uneven and uncomfortable in use.